1. Field of the Invention
The invention relates to a control device including a multi-layer circuit board in which a plurality of circuit conductors and a plurality of insulating layers are stacked such that each of the insulating layers is interposed between the adjacent circuit conductors, and relates to a vehicle steering system including the control device.
2. Description of Related Art
Conventionally, as a control device used in a vehicle steering system or the like, a control device that controls the operation of an electric motor has been known. This control device includes a circuit board having a control circuit that outputs a control signal, and a drive circuit that controls the on/off states of switching elements such as FETs in response to the control signal, so as to supply a drive current to the electric motor. Further, in recent years, in order to reduce the size of a circuit and to increase the density of the circuit, there have been employed circuit boards having a multi-layer structure in which a plurality of circuit conductor layers on which circuit patterns are formed, and a plurality of insulating layers are stacked such that each of the insulating layers is interposed between the adjacent circuit conductor layers.
As an example of the control device as described above, a control device is described in Japanese Patent Application Publication No. 2011-83063 (JP 2011-83063 A). In the control device described in JP 2011-83063 A, a control circuit portion, in which a control circuit pattern constituting lines of a control circuit is formed, and a drive circuit portion, in which a drive circuit pattern constituting lines of a drive circuit is formed, are formed respectively in separate areas on a single circuit board having a multi-layer structure, that is, the control circuit and the drive circuit are formed on one circuit board. The control device described in JP 2011-83063 A has an advantage that the size of the control device can be easily reduced, as compared to a control device in which the control circuit and the drive circuit are formed respectively on separate circuit boards that are connected to one another by a connection component such as a bus bar.
In recent years, there have been demands for further reducing the size of the control device. However, in the configuration described in JP 2011-83063 A, the entire control circuit portion and the entire drive circuit portion are formed on the single circuit board in the form of a flat plate. Thus, it is difficult to reduce the size of the circuit board in a planar direction, and accordingly, it is difficult to reduce the size of the control circuit board in the control device.